The use of a single assembly for mounting on a seeder and dispensing both fertilizer and seed in a single pass is known from prior U.S. Pat. No. 4,762,075 of one of the present inventors (Halford) and from subsequent U.S. Pat. Nos. 5,331,907 and 5,396,851 of Beaujot.
These assemblies generally include a furrowing element or knife for producing a furrow in the ground as the assembly is pulled across the ground and a fertilizer feed tube for depositing fertilizer directly behind the furrowing element. A second delivery member including a dispensing tube is provided spaced rearward and laterally offset from the furrowing element for depositing the seed in ground spaced at a position offset to one side from the fertilizer and preferably offset above. A packer wheel then follows for packing more earth above the seed.
A biasing element is generally provided for urging both the furrowing element and the packer wheel downward to engage the earth. In some known assemblies however the forces are more directed to one element rather than the other. When the forces are not properly distributed the resulting seeding operation becomes less effective. The arrangement shown in the above patent of Halford provides an arrangement using a shank for applying force to the knife and a separate spring for applying forces to the packer and second delivery member. In practice both are adjustable to provide independent adjustment of the separate forces for best control. The known assemblies of Beaujot provide instead an arrangement using hydraulic cylinders to apply the force. However these do not allow the distribution of force between the packer wheel and the second distribution member on one assembly and the furrowing element or knife on a second assembly to be adjusted independently and thus the seeder is less suited to varying conditions of the ground to be seeded.
The arrangement of Halford also uses a spring as a connection between two parts of a tube to allow flexibility of the tip end of the second delivery member. While this provides an inexpensive construction which allows the required operation, it does in some situations have a limited life as the spring is required to flex in a direction that tends to concentrate forces in one part of the spring leading to premature breakage at that location.